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System that measures absolute or additive phase noise includes a power divider for dividing an input RF signal, a local oscillator, two mixers, each arranged in a path of a respective signal component from the power divider and receiving input from the power divider and local oscillator, two digital

System that measures absolute or additive phase noise includes a power divider for dividing an input RF signal, a local oscillator, two mixers, each arranged in a path of a respective signal component from the power divider and receiving input from the power divider and local oscillator, two digital radio frequency memories, each associated with a respective mixer and receiving an input signal therefrom, and a digital signal processor that receives signals from the digital radio frequency memories and outputs a digital data stream indicative of measured phase noise. For absolute phase noise measurement, phase noise of the input RF signal is provided. For additive phase noise measurement, a unit under test is arranged in one of the paths between the power divider and the mixer. The system may be interposed between a radar transmitter of a radar environment simulator and a radar receiver coupled to a radar target display.

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1. A system that measures phase noise, comprising: a local oscillator;a power divider for dividing an input RF signal from a source other than said local oscillator into two signal components that are output therefrom;two mixers, each arranged in a path of a respective one of the signal components f

1. A system that measures phase noise, comprising: a local oscillator;a power divider for dividing an input RF signal from a source other than said local oscillator into two signal components that are output therefrom;two mixers, each arranged in a path of a respective one of the signal components from said power divider, each mixer receiving a respective one of the signal components from said power divider and a signal from said local oscillator; anda data acquisition and digital analysis subsystem that receives analog signals from said mixers, converts the analog signals into digital signals and analyzes the digital signals,said data acquisition and digital analysis subsystem comprising: two digital radio frequency memories, each associated with a respective one of said mixers and receiving an input signal therefrom; anda digital signal processor that receives signals from said two digital radio frequency memories and outputs a single digital data stream indicative of measured phase noise. 2. The system of claim 1, wherein said digital radio frequency memories are used together to ensure that pipeline delays of analog to digital conversion of the analog signals from said mixers are managed to keep the relative RF delay near a range of 1 msec. 3. The system of claim 1, further comprising a test set controller that converts information provided by or derived from digital analysis of said radio frequency memories into commands to change operation of the system or components thereof. 4. The system of claim 1, wherein the system is used to measure absolute phase noise of the input RF signal being provided to said power divider and said digital radio frequency memories are configured to apply a different phase shift to the input signal being received by each of said digital radio frequency memories, said digital signal processor performing a digital down-conversion of said phase shifted signals and outputting the single digital data stream that represents a down-converted baseband containing phase noise content. 5. The system of claim 4, further comprising a display coupled to said digital signal processor and configured to display the down-converted baseband as measured phase noise content. 6. The system of claim 3, wherein said test set controller is configured to control the RF signal source that provides the input RF signal to said power divider and the system is configured to measure phase noise added by a unit under test when arranged between said power divider and one of said mixers. 7. The system of claim 1, wherein the system is configured to measure phase noise added by a unit under test when arranged between said power divider and one of said mixers and each of said digital radio frequency memories is configured to store received signals as in-phase and quadrature (I/Q) data, preserving a phase relationships of the received signals, whereby said digital radio frequency memories enable matching of signal paths thereby replicating the phase shift such that output from said digital signal processor is a set of data depicting additive phase noise present in a signal path including the unit under test. 8. The system of claim 6, further comprising a master clock that provides clock signals to said local oscillator and said digital radio frequency memories. 9. The system of claim 6, wherein said RF signal source is configured to generate a pulse modulated RF signal. 10. A radar environment simulator, comprising: a radar transmitter;a radar target display;a radar receiver that generates and provides signals to said radar target display to enable said radar target display to display a simulated target and clutter; anda phase noise test and diagnostic unit including the system of claim 1, said digital radio frequency memories being configured to receive a transmitted RF sample from said radar transmitter and output a simulated environment to said radar receiver;said test set controller being further configured to process feedback based on the simulated target and clutter on said radar target display and control said digital radio frequency memories. 11. The simulator of claim 10, wherein said test set controller is further configured to derive a radar phase noise floor as a function of clutter range factor and loss of target detection. 12. A method for measuring phase noise, comprising: dividing an input RF signal into two signal components using a signal divider;arranging a respective mixer in a path of each of the signal components, each mixer receiving a respective one of the signal components from the power divider and a signal from a local oscillator, the input RF signal divided by the signal divider being from an RF signal source different than the local oscillator;providing analog signals from the mixers to a data acquisition and digital analysis subsystem that converts the analog signals into digital signals and analyzes the digital signals;arranging a digital radio frequency memory in the data acquisition and digital analysis subsystem in a path from each of the mixers such that each digital radio frequency memory receives an input signal therefrom; andreceiving signals from the two digital radio frequency memories at a digital signal processor in the data acquisition and digital analysis subsystem that outputs a single digital data stream indicative of measured phase noise. 13. The method of claim 12, further comprising converting information provided by or derived from digital analysis of the digital radio frequency memories into commands at a test set controller. 14. The method of claim 12, wherein absolute phase noise of the RF signal being input to the power divider is measured, further comprising arranging the digital radio frequency memories to apply a different phase shift to the input signal being received by each of the digital radio frequency memories and configuring the digital signal processor to perform a digital down-conversion of the phase-shifted signals and output the single digital data stream that represents the down-converted baseband containing phase noise content. 15. The method of claim 14, further comprising coupling a display to the digital signal processor and displaying the down-converted baseband as measured phase noise content thereon. 16. The method of claim 12, wherein additive phase noise is measured, further comprising: arranging an RF signal source to provide the input RF signal to the power divider; andpositioning a unit under test that adds phase noise between the power divider and one of the mixers such that phase noise added by the unit under test is measured. 17. The method of claim 16, wherein each of the digital radio frequency memories stores received signals as in-phase and quadrature (I/Q) data, preserve a phase relationships of the received signals, whereby the digital radio frequency memories enable matching of signal paths thereby replicating the phase shift such that output from the digital signal processor is a set of data depicting additive phase noise present in a signal path including the unit under test. 18. The method of claim 16, further comprising providing a master clock that generates clocks signals for the local oscillator and the digital radio frequency memories. 19. The method of claim 16, wherein the RF signal source is configured to generate a pulse modulated RF signal. 20. The system of claim 1, wherein said data acquisition and digital analysis subsystem is configured to apply a phase shift to a signal being processed by one of said digital radio frequency memory relative to a signal being processed by the other of said digital radio frequency memory depending on a type of phase noise being measured.